German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) satellite communication researchers have demonstration a new data compression technology for the first time. This demonstration was made possible using network coding, which reduces transmission bandwidth requirements. The process has applications, for example, in emergency response, when local networks fail and emergency services have to fall back on satellite communications. For internet and cellular traffic, data is transmitted over terrestrial links and network coding is used sometimes, but it is new for satellite communications.

Satellite terminals in Sardinia and Oberpfaffenhofen

This new technology, based on a proposal published by Rudolf Alswede, Ning Cai, Shuo-Yen Robert Li and Raymond W. Yeung, was implemented by researchers at the DLR Institute of Communications and Navigation and demonstrated for the first time over a satellite link on 14 September 2010. The demonstration took place at the Advanced Satellite Multimedia Systems Conference in Cagliari, Sardinia, and used videoconferencing as its test medium. The data were transmitted between two satellite terminals, in other words, two send/receive stations, one in Cagliari and the other at DLR Oberpfaffenhofen. The data were first sent to the satellite, which forwarded them to a terrestrial gateway station. This was where network coding came into play; the gateway modem bundled incoming data packets from both terminals together into a single packet, but this did not result in a packet with a size equal to the sum of the two. The resulting data packet was only slightly larger than each of the incoming packets.

For example, if the gateway receives two packets of 1000 bits each, network coding bundles them together into a packet of around 1100 bits – thus reducing the overall incoming data size of 2000 bits by 45 percent. Satellite service providers calculate their fees based on the amount of bandwidth users consume, in other words, the number of bits transmitted – so that users save money by compressing their data. The gateway sends the new packet back to the satellite, which sends it on to the satellite terminals. Since the terminals know what data they have sent, they can extract the answering packet sent by the other terminal from the network-coded bundle.

Network-coded videoconference using the Eutelsat Eurobird 3 satellite

"Network coding is a very interesting option for satellite communications. In contrast to cable or cellular communications, it is often the case in satellite communications that both partners also receive the other party’s data, so network coding leads to significant savings. Furthermore, satellite communications are very price critical. Any savings are crucial and increase the range of potential applications. At DLR we're working on developing this technology even further – we'll soon have more announcements to make," says Prof. Christoph Günther, Director of the DLR Institute of Communications and Navigation. For their demonstration, the DLR researchers used the Eutelsat Eurobird 3 satellite. DLR's German Space Operations Center (GSOC) supported the project.

The project was sponsored by the DLR Space Agency with funds from the German Federal Ministry for Economics and Technology (Bundesministerium für Wirtschaft und Technologie; BMWi), under a mandate from the German Federal Government.